With the advantages of high image quality, power saving, thin bodies, wide application range and the like, liquid crystal displays (LCDs) have been widely applied to various consumer electronic products such as mobile phones, televisions, personal digital assistants, digital cameras, notebook computers and desk computers, and have become the mainstream of display devices. The LCDs are based on the amorphous silicon (A-Si) display technique or the low-temperature poly-silicon (LTPS) display technique, and LTPS has the advantages over A-Si of high resolution, wide view of angle and the like. In the long-time research and development process, the inventor of this application realized that poly-silicon (poly-Si), prepared through traditional processes, in LTPS products is high in surface roughness, consequentially, affecting the reliability of the products.
Particularly, according to one preparation method, after an amorphous silicon thin film is formed, an oxide film naturally formed on a surface of the amorphous silicon thin film is completely etched away with hydrofluoric acid; and then oxidization is carried out with ozone to form a new oxide film; after the amorphous silicon thin film is dried, excimer laser treatment is carried out on the amorphous silicon thin film to obtain a poly-silicon thin film. However, the poly-silicon thin film obtained through this method is high in surface roughness, for instance, the roughness R of the poly-silicon thin film reaches 11.5 nm. Please refer to FIG. 1 for details, FIG. 1 is a schematic view of a surface of a poly-silicon thin film in the related art.
Particularly, according to another preparation method, after an amorphous silicon thin film is formed, an oxide film naturally formed on a surface of the amorphous silicon thin film is completely etched away with hydrofluoric acid; then excimer laser treatment is carried out on the amorphous silicon thin film twice, and after excimer laser treatment is carried out on the amorphous silicon thin film for the first time, a uniform and thin oxide film is formed on the surface of the amorphous silicon thin film, specifically, during the first time of excimer laser treatment, the amorphous silicon thin film is rapidly scanned with lasers in an atmosphere containing a small quantity of oxygen so as to form the oxide film, and then excimer laser treatment is carried out on the amorphous silicon thin film for the second time to form a poly-silicon thin film. The oxide film formed through this method is thin, and the roughness is reduced by shortening the extrusion time in the recrystallization process (namely reducing protrusions), for instance, the roughness R is 5.6 nm. Please refer to FIG. 2 for details, FIG. 2 is a schematic view of a surface of another poly-silicon thin film in the related art. However, this method has a high cost.